Ultrastructural aspects of hepatic coccidiosis caused by Goussia lusca n. sp. (Apicomplexa: Coccidia) infecting Trisopterus luscus (Gadidae) from the NE Atlantic Ocean

Goussia lusca n. sp. is described from the liver of pouting Trisopterus luscus from the NE Atlantic Ocean in Ibero-Atlantic Portuguese and Spanish waters. Mature oocysts were 31.7 (28.8 to 35.4) microm in diameter. Each oocyst contained 4 ellipsoidal sporocysts arranged in an aleatory position, and measuring approximately 13.7 x 9.2 microm. Each sporocyst contained 2 sporozoites. Ultrastructurally, the sporocyst wall consisted of a dense inner layer 115 nm thick, transversely striated, regularly intercalated by thin grooves with electron-lucent spaces, and separated from the outer layer by a thin, light (electron-lucent) space. The outer layer was multilamellated and consisted of parallel dense bands alternating with light spaces. These lamellae formed filamentous extensions of the wall. The dehiscence suture, a characteristic feature of the genus, was present in the sporocysts. No external clinical signs were observed in the host fish. Parasites observed in the liver tissue were often enveloped in a yellowish-brown matrix, generally known as 'yellow bodies'. Sometimes sporocysts were observed in direct contact with the liver cells. Parasites in degeneration and aggregations of amylopectin granules were frequently observed surrounded by host inflammatory cells. In severe infections, we observed large agglomerations of oocysts encapsulated by layers of concentrically arranged connective tissue forming large granulomas, which caused significant replacement of the host liver parenchyma by the parasite.